Question 1

ExVCR vs Mox for Elixir HTTP mocking

Accepted Answer

ExVCR records and replays real HTTP interactions as JSON cassettes, ideal for deterministic tests with exact responses. Mox, on the other hand, is a behavior-based mocking library that doesn't rely on recordings, offering more flexibility for dynamic mocking but requiring manual setup. Choose ExVCR if you need to capture real API calls; use Mox for finer control over mock logic.

Question 2

How to filter sensitive data in ExVCR cassettes

Accepted Answer

Use ExVCR.Config.filter_sensitive_data to define patterns (like passwords) and replace them with placeholders in recorded cassettes. This ensures that sensitive information isn't stored in test files, and you can apply it to URLs, headers, and bodies as shown in the README examples.

Question 3

Does ExVCR work with Phoenix applications?

Accepted Answer

Yes, ExVCR can be used in Phoenix apps by adding it as a test dependency and configuring it for HTTP clients like HTTPoison or Finch. However, ensure your HTTP client is supported and be mindful of performance impacts in large test suites.

Question 4

How to handle dynamic API responses with ExVCR

Accepted Answer

For dynamic responses, use custom cassettes or stubbing features to manually define JSON responses, or leverage custom matchers to match requests flexibly. This allows you to simulate varying data without recording new cassettes for each test run.

Question 5

ExVCR performance issues and solutions

Accepted Answer

ExVCR can slow down tests due to cassette recording and replay overhead. The README suggests enabling the experimental global mock feature to reduce latency, but it's unstable. Alternatively, limit cassette use to critical tests or consider complementary tools like Mox for faster mocking.

Question 6

Setting up ExVCR for multiple test environments

Accepted Answer

Configure ExVCR in your config/test.exs file with settings like cassette directories and sensitive data filters. Use mix tasks to manage cassettes across environments, and ensure adapters are set correctly based on the HTTP client used in each environment.

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